In a large cast iron skillet over medium heat, heat the olive oil. Add the diced onion and cook, stirring frequently, until translucent, about 2-3 minutes. Stir in the minced garlic and cook until fragrant, approximately 1 minute.
Pour in the white wine, scraping any browned bits from the bottom of the skillet.
Add the thawed and drained spinach, chopped artichoke hearts, and crushed red pepper flakes. Stir until warmed through and any excess liquid has evaporated, about 4 minutes.
Reduce the heat to low. Stir in the cubed cream cheese until melted and well combined. Mix in the sour cream and freshly grated Parmesan cheese until the mixture is smooth and creamy. Season with kosher salt and freshly ground black pepper to taste.
Sprinkle the shredded mozzarella cheese evenly over the top of the mixture. Transfer the skillet to the oven and broil until the cheese is bubbly and golden brown, about 2-3 minutes.
Remove from the oven and let it cool slightly before serving. Pair with tortilla chips, pita chips, crostini, or your preferred dipping items.